This invention relates to an electrophotographic photoreceptor, and more particularly to an electrophotographic photoreceptor using an organic photoconductive material.
Generally used as photoconductive materials for electrophotographic photoreceptors are inorganic materials such as selenium (Se), cadmium sulfide (CdS), zinc oxide (ZnO), amorphous silicon (a--Si) and the like. Photoreceptors using such inorganic photoconductive materials are used in such a manner that the photoreceptors are charged in the dark by means of, for example, a charging roller and then subjected to image-wise exposure to selectively neutralize the charges only on the exposed portions, and the electrostatic latent image thus formed is thereafter visualized with a developer to form an image. Such photographic photoreceptors are basically required to have (1) an ability to be charged to an adequate potential in the dark and (2) a function of neutralizing the surface charges by exposure to light. However, the above-mentioned inorganic photoconductive materials have merits and demerits and, for example, selenium (Se) satisfies sufficiently the requirements (1) and (2) but is inflexible and difficult to mold into a film. In addition, it is sensitive to mechanical impact and hence must be carefully handled. Amorphous silicon (a--Si) has such a demerit that severe production conditions are required and hence its production cost becomes high.
Recently, function-separated type organic photoreceptors have been mainly used which have a charge-generating layer consisting of a phthalocyanine compound or an azo compound which is known as an organic photo-conductive material having laminated thereto a charge-transfer layer consisting of a hydrazone compound or the like.
In such organic photoreceptors, charge-transfer materials which are effective to a specific charge-generating material are not always effective to other charge-generating materials. That is, it is necessary to adequately combine a charge-generating material with a charge-transfer material, and if the combination is inadequate it will be impossible to obtain an electrophotographic photoreceptor excellent in characteristics such as sensitivity and the like.
On the other hand, a laser printer has recently been extensively developed which uses as a light source a semiconductor laser having a wavelength in the near infrared region. The electrophotographic photoreceptors applied to this field are required to have high sensitivity to light having a wavelength in the oscillatory wavelength region of a semiconductor laser (about 760-850 nm), and simultaneously, a short response time which is the time required until the charges are neutralized by exposure to light becomes a great factor required for the photoreceptor.
For meeting said requirement, attention is directed to a phthalocyanine compound among charge-generating materials because it is sensitive to semiconductor wavelength region.
Of phthalocyanine pigments, metalophthalocyanine compounds have been much studied, and hydroxytitanium phthalocyanines having different crystal forms have been reported as particularly useful compounds. However, the film formed from the above phthalocyanine is chemically instable, and when it is contacted with, for example, a solvent its crystal form is changed, whereby a great difference is caused in respect of electrophotographic characteristics such as charge potential, residual potential and the like. A solution of this problem has been strongly desired.
However, there have been found neither phthalocyanine compounds as charge-generating materials excellent in electrophotographic characteristics in the oscillatory wavelength region of semiconductor laser nor charge-transfer materials to be adequately combined with the phthalocyanine compounds.
In order to solve the above problems of prior art, the present inventors have made extensive research on various organic compounds as the charge-transfer materials to be combined with the phthalocyanine compound as the charge-generating material to find that a specific butadiene compound is very effective to enhance the electrophotographic characteristics, and as a result, have obtained a photoreceptor having high sensitivity and excellent light responsibility.